Method of making glass-ceramic matrix using closed tubes

ABSTRACT

Disclosed is an assembly or matrix comprising an arrangement of integrally fused tubes forming a series of nonporous, longitudinal parallel passageways therethrough. The matrix is of a low-expansion ceramic material and the passageways therethrough have thin walls; a high proportion of the cross-sectional or frontal area of the matrix is free open area. Also disclosed are methods for making such a matrix from glass tubes that are thermally crystallizable; one method involves longitudinally bundling the tubes with their ends sealed and heating the assembly to soften, expand and fuse the tubes in a heat treatment schedule that also nucleates and thermally crystallizes the matrix to the final ceramic product. Another embodiment involves superimposing a plurality of layers of tubes, one layer above the other in successive parallel planes, with the tubes in each plane being essentially parallel to each other and transverse to the tubes in adjacent layers. The matrix of tubes, each with its ends sealed, is heated to soften, expand and fuse the tubes. The sealed ends are opened and a plurality of such matrices are assembled into an annular structure, each matrix being separated from adjacent matrices by a wedge-shaped member.

United States Patent [1 1 Mar. 18, 1975 Pei l l METHOD OF MAKINGGLASS-CERAMIC MATRIX USING CLOSED TUBES [75] Inventor: Yu K. Pei,Toledo, Ohio [73] Assignee: Owens-Illinois, Inc., Toledo, Ohio [22]Filed: May 5, 1972 [21] Appl. No.: 250,550

Related U.S. Application Data [63] Continuation of Ser. No. 146,665, May25. 1971, which is a continuation-in-part of Ser. No. 30,859, April 22,1970. abandoned.

[52] U.S. Cl 65/4, 65/33, 65/DIG. 7, 65/DIG. 9 [SH Int. Cl. C03c 23/20,CO3c 29/00 [58] Field of Search 65/4, 33, DIG. 4, DIG. 9, 65/DIG. 7

[56] References Cited UNITED STATES PATENTS 3.269.8l7 8/1966 Bondley65/4 3,Z79 93l Ill/I966 Olcott 65/33 X 3,331.671) 7/1967 Cole 65/43,5l-L275 5/l970 Bray l 65/33 3,582.3Ul 6/l97l Andrysiak et al.... 65/4X 3.582.385 -l/I97l Duke et al. 65/33 3.773.484 ll/l973 Gray. .lr. 65/33Primary E.\uminerS. Leon Bashore Arsislun! Examiner-Frank W. MigaAttorney, Agent, or Firm-Charles S. Lynch; E. J.

Holler [57] ABSTRACT Disclosed is an assembly or matrix comprising anarrangement of integrally fused tubes forming a series of nonporous,longitudinal parallel passageways therethrough. The matrix is ofalow-expansion ceramic material and the passageways therethrough havethin walls; a high proportion of the cross-sectional or frontal area ofthe matrix is free openarea. Also disclosed are methods for making sucha matrix from glass tubes that are thermally crystallizable; one methodinvolves longitudinally bundling the tubes with their ends sealed andheating the assembly to soften, expand and fuse the tubes in a heattreatment schedule that also nucleates and thermally crystallizes thematrix to the final ceramic product. Another embodiment involvessuperimposing a plurality of layers of tubes, one layer above the otherin successive parallel planes, with the tubes in each plane beingessentially parallel to each other and transverse to the tubes inadjacent layers.

'The matrix of tubes, each with its ends sealed, is

heated to soften, expand and fuse the tubes. The sealed ends are openedand a plurality of such matrices are assembled into an annularstructure, each matrix being separated from adjacent matrices by awedge-shaped member.

19 Claims, 19 Drawing Figures PATENTEU 1 8 i 75 SHEET 2 BF 5 PATENTEDMAR] 81975 SHEET H UF 5 METHOD OF MAKING GLASS-CERAMIC MATRIX USINGCLOSED TUBES This is a continuation of applicants copending applicationSer. No. 146,665, filed May 25, 1971, which in turn is acontinuation-in-part of applicants copending application Ser. No.30,859, filed Apr. 22, 1970, the latter now abandoned.

This invention relates to an assembly or matrix of fused ceramic tubesideally suited for a variety of uses and applications, and moreparticularly as a compact regenerative heat exchanger. Morespecifically, the matrix of this invention is useful in gas turbineengines designed for fuel economy when the engine is operating at lessthan full power. Another use for the article of this invention is as aburner screen in a Bunsen or Fisher burner. The invention also relatesto a method for making such assembly.

Gas turbine engines offer potentially significant advantages over pistonengines for automobile and truck use. Well designed gas turbine enginesproduce extremely low amounts of air pollutants because such enginesoperate at high temperatures and at high air-fuel ratios, therebyeffecting essentially complete combustion. The use of only one sparkplug and the use of nonleaded fuels further insure minimizing oreliminating lead. Gas turbine engines are lighter in weight and morecompact than piston engines of comparable power. Also, reliability isgreater and maintenance cost of gas turbines is less than with pistonengines because the engine is simpler, having fewer moving parts.

However, the fuel efficiency of gas turbine engines at less than fulldesign loads, as for example, in stop and go driving in automobiles andtrucks, is not yet sufficiently high for them to be competitive withpiston engines for automobile and truck use. Much effort has beendirected toward increasing the efficiency of gas turbine engines, thatis, to providing means forconverting a larger proportion of thecalorific content of the fuel into energy. Since most of the wastecalories come out of the exhaust in the form of heat, the efficiency ofthe engine can be increased if this waste heat is returned to the workcycle. It has been proposed to accomplish this by rengerative heatexchangers, which in one form are foraminous discs of heat-retainingmaterial that rotate in the engine exhaust gases and convey heat fromthe exhaust gases to the incoming air.

Requirements for a successful regenerator are so stringent that theyhave not been completely satisfied by currently available structures.Thermal properties necessary for the regenerator include a. ability towithstand inlet temperatures at least as high as 1450 F. for extendedperiods of time;

b. high thermal shock resistance so that the structure will withstandengine start-up when it is subjected to a sudden temperature elevationfrom ambient temperature to temperatures on the order of l400l500 F.,and will not be ruptured or distorted by the temperature gradient acrossthe regenerator, which may be as high as l400 F. at a cold start and 900F. in a steady state operation;

c. low coefficient of thermal expansion to minimize any distortion ofthe precisely dimensioned rotary wheel under the aforementioned thermalgradients;

d. high heat capacity (product of specific heat and density); and

e. low thermal conductivity, to prevent the flow of heat through thematerial comprising ther-egenerator in a direction perpendicular to theflow of the hot gases, and, most importantly, to minimize the conductionof heat along the length of the tubes in order to obtain most efficientheat exchange with the flowing gases from cycle to cycle.

Regenerator structures must have high surface area to achieve good heattransfer. However, the friction generated by the gases passing throughthe structure must be low since energy expended in overcoming frictionrepresents lost horsepower. To minimize pressure drop across theregenerator, the regenerator should have a multiplicity of parallel,smooth, and unobstructed passageways extending through it and shouldhave a high percentage of open or free frontal area. The walls of suchpassageways should be nonporous to the gases flowing through thepassageways. Such passageways preferably should not contain any twoadjacent surfaces which meet at an acute angle since the passagewayformed by such an acute angle causes high frictional losses which aredetrimental to the operation of the regenerator.

In operation, the air and exhaust gas sections of a rotating regeneratorare separated by a stationary seal bar which is in contact with and rubsagainst the face of rotating regenerator wheel. Since abrasion andmechanical shock can be caused by the seal bar, the regenerator surfaceshould also have good wear resistance and a low coefficient of friction.

Some regenerators have been and are formed from metals. However, thehigh coefficient of thermal expansion of such metals and the resultantdistortion under thermal gradients is a serious drawback to their usefor this purpose. Also, and more importantly, since the thermalconductivity of metals is so great, the desirable high thermal gradientin the matrix material from the hot to the cold face is difficult toachieve. Thus, a maximum temperature difference along the lengths of thetubes is important from the standpoint of efficiency of heat transferwith the gases.

Other regenerators are formed by a lost paper process in which paper iscoated with a ceramic slurry containing a thermosetting plastic binder,corrugated with hot rolls, shaped into a wheel configuration, and thenburned out during fusion of the ceramic, leaving the ceramic sheelformed of sintered particles. However, preparation of regenerators byparticle-sintering results in a porous structure. Porosity lowers thestrength, decreases the heat capacity of the structure and increasesfriction loss. Also, in thin-walled regenerator structures, many of thepores extend from one wall through to the opposite wall, and provide anundesirable permeability of the gases through the walls.

Widespread use of gas turbine engines for automobiles and trucks isdependent upon development of a successful regenerator.

Accordingly, it is an object of this invention to provide a structure ormatrix of superior properties, and especially a matrix capable of use asa gas turbine regenerator which does not have the aforementioneddeficiencies of previous regenerators.

Another object of this invention is to provide a matrix having a lowcoefficient of linear expansion, low thermal conductivity, and which iscapable of withstanding temperatures of the order of 1450 F. for longperiods of-time,'-and temperatures of 1800 F. to l950' F. and higher forshorter periods.

Another object of the invention resides in such a ceramic matrix in.theform of a honeycomb structure wherein the longitudinal passagewayshave in crosssection a substantially hexagonal configuration. This is aparticularly strong configuration'and, of course, adjacent heatexchangesurfaces or walls meet at obtuse angles, thereby minimizing pressuredrop during flow of gases through the passageways.

Still another object is to provide an assembly or matrixstructure havingatmultiplicity of thin-walled parallel, smoothand. unobstructedpassageways, which structure has a high percentage of free frontal areaand a high surface area, but which produces relatively little frictionalloss of pressure when gases are passed therethrough.

Another object of the present invention is to provide a process formaking the aforementioned structure or matrix.

A further object of this invention is to provide an assembly or matrixhaving a plurality of layers of tubes which are superimposed one abovethe other in successive parallel planes, the tubes within each planebeing essentially parallel to each other and transverse to tubes inadjacent layers, each tube being integrallyfused to each adjacentparallel tube and each adjacent transverse tube, which assembly ormatrix is suitable for use in a cross-flow regenerator.

Still a further object of this invention is to provide a process forassembling a layer or ribbon consisting of a plurality of tubes disposedin parallel relationship, with each tube longitudinally adhering to eachtube adjacent thereto, wherein said layer or ribbon of tubes is thenutilized in quickly and economically assembling a matrix for use in across-flow recuperator.

Other objects, as well as aspects and advantages of the invention willbecome apparent from a study of this specification and the drawings.

According to one aspect of the invention there is provided an assemblyor matrix comprising a bundle of integrally fused tubes forming a seriesof smooth, longitudinal, parallel passageways therethrough, wherein thewalls defining said passageways:

l. have. essentially zero porosity,

2. consist essentially of an inorganic crystalline oxide ceramicmaterial,

3. have an average coefficient of lineal thermal expansion of about 12to +12 10"/C. over the range 300C. and preferably -5 to +5 X l0" /C.over such range,

4. have a maximum inner diameter of 0.1 inch, and

5. have a wall thickness of about 0.03 to 0.002 inch through portions ofsuch walls common to adjacent tubes, the ratio of said inner diameter tosaid thickness being at least 3, and wherein the thermal conductivity ofthe ceramic material of said matrix is substantially less than metal andpreferably less than 0.01 cal/cm /sec/cm/C. at 400 C., and the openfrontal or cross-sectional area is at least 60 percent of thecross-sectional area of the matrix. The surface density of such a matrixis at least 270 square feet per cubic foot of matrix. As used herein,surface density is defined as the total square feet of wall surface areaper cubic foot of the assembly or matrix.

, ,-Since the matrix has an open frontal area of atleast about 60percent, thesum of the cross-sectional areas of the walls defining thepassageways is at most 40 percent of the total frontal orcross-sectional area of the matrix structure. 7 I

For most applications matrices having the foregoing properties buthaving a ratio of the inner diameter of the tubes or passageways to wallthickness of at least 3.6 and having an open frontal or cross-sectionalarea of at least 65 percent of the matrix cross-sectional area arepreferred, because in applications such as in a gas turbine regenerator,for instance, the increased open area minimizes pressure drop and alsoincreases surface density, which latter property increases the heattransfer rate to and from the gases passing there through. The surfacedensity of 'such preferred matrix structures is at least 295 square feetper cubic foot of matrix. i

Moreover, for the embodiments of the matrix structure of the inventionjust described, i.e., wherein the Various types of regenerator matriceshave beenmade in the past from metal. One important advantageof thepresent matrices is that the very low thermal conductivity of theessentially crystalline inorganic oxide ceramic material, as compared tometal, results in a much higher temperature gradient from inlet tooutlet ends of the passageways of the matrix, when used as aregenerativeheat exchanger. This is very important, since the hotcombustion gasesflow through the matrix passageways in one direction, and the incomingair flows through in the opposite direction. The cold air thus contactsthe cooler end of the matrix first and the hotter end last. The greaterthe temperature difference from the inlet to outlet sides of the matrixthe greater the driving force for transfer of heat from the matrix tothe air or combustion gases, and thus the greater the efficiency of heatrecovery.

It should be noted that in the first matrix structuredescribed'hereinbefore the ratio of the inner diameter to the thicknessof the portions of walls common to adjacent passageways is 3, and thatthe thickness of the portions of the walls common to the adjacentpassageways is from 0.03 to 0.002 inch. When reading the descriptionhereinafter of a corresponding process suitable for makingithe newmatrix structures, it will be noted that the starting material tube wallthickness is about 0.015 to about 0.001 inch for the individual startingmaterial tubes, and that the ratio of the inner diameter of such tubesto such wall thickness is at least than twice the thickness whenmeasurable expansion of the tubes is effected during the fusion process.

Y As used in the structure claims of this invention, the term innerdiameter refers. to the shortest distance through the center of the tubeor passageway from one inner wall to the opposite inner wall. Thisdistance is the same for all diameters of a circle, of course, but for 4to that of FIG. 4 wherein the rim is provided with a sehoneycombstructure comprising an aggregation of integrally fused tubes havinglongitudinal passageways which in cross-section have substantiallyhexagonal configuration, which configuration results in adjacent heatexchange surfaces meeting at obtuse angles. See FIG. 6.

According to one embodiment of the invention, a novel method is providedwhich is suitable for preparing the desired foraminous ceramicstructures of the invention. Such method comprises assembling aplurality of thin, elongated, hollow, thermally crystallizable glasstubes in closely packed, parallel relationship, each of the tubes havinga fluid medium sealed therein, and subsequently heat-treating theassembly of tubes and thereby causing (l) the tubes to soften, (2) thefluid medium to expand the tubes outwardly so that adjoining contactingsurfaces of the tubes fuse together to form a unitary structure and (3)the tubes to thermally in situ crystallize to form an at least partiallycrystalline inorganic oxide ceramic material commonly referred to in theart as a glass-ceramic. The expansion of the tubes by the fluidexpansible medium seal'ed therein is important from two aspects. First,even if the actual expansion or reshaping of the tubes by the pressureof'the hot expansible medium or gas is small, the pressure exertedforces adjacent surfaces into contact and is important to obtainingproper fusion of the tubes. Secondly, where desired the expansion can beeffected to expand and reshape circular tubes, for instance, into adesirable hexagonal shape.

Other features of the invention will become apparent to those skilled inthe art from a consideration of the following detailed description takentogether with the drawings, wherein:

FIG. 1 is a perspective view of a jig assembly utilized in making anembodiment of the structure of the invention and showing a partialpacking of tubes within the structure mounted on the assembly;

FIG. 2 is a side view of a glass tube used in making the structure ofthe invention;

FIG. 3 is an enlarged cross-sectional view of the glass tube taken alongline 3-3 of FIG. 2;

FIG. 4 is a partial cross-sectional view of the structure of theinvention of Flg. l placed within an assembly prior to heat treatment;

FIG. 5 is a top plan view of a portion of the structure of theinvention, greatly enlarged, showing the arrangement of the glass tubesprior to being expanded by heat treatment;

FIG. 6 is a top plan view of a small portion of the structure of theinvention, greatly enlarged, showing the arrangement of the glass tubesafter they have been expanded and crystallized by heat treatment;

FIG. 7 is a top plan view of another embodiment of a rotary heatexchanger of the invention;

FIG. 8 is a cross-sectional view of the heat exchanger taken along lines8-8 of FIG. 7;

FIG. 9 is a perspective view of another embodiment of the heat exchangerof the invention;

ries of recesses adapted to receive and engage driving means for thestructure;

FIG. 11 is a perspective view of still another embodiment of theinvention;

FIG. 12 is atop plan view of a modification of the embodiment of FIG.llwherein'rec esses are provided at the outer periphery thereof, whichrecesses are adapted to receive and engage driving means for thestructure;

FIG. 13 is a side elevation in cross-section of a gas burner utilizingthe structure of the invention;

FIG. 14 is a perspective schematic view of another embodiment of thematrix of the invention showing an enlarged arrangement of tubes inalternate layers with the tubes in each layer parallel'to each other andtransverse to tubes in adjacent layers;

and fused together;

FIG. 16 is an isometric view of a regenerator formed with a plurality ofmatrix segments having the arrangement illustrated in FIG. 14;

FIG. 17 is an expanded view of a portion of the regenerator illustratedin FIG. 16;

FIG. 18 is a plan view of apparatus utilized in making the ribbon ofparallel tubing; and v FIG. 19 is an enlarged perspective view of aportion of the apparatus of FIG. 18 showing the pair of burners fusingand sealing the ends of the tubes.

As illustrated in FIG. 1, a ceramic'rim 10 is mounted on a jig 11comprising a face board 12 attached to a conventional vibrator 13. Threeclamping means 14 are spaced about the edges of face board 12 andremovably secure the rim 10 thereto. Each of clamping means 14 comprisesa stem portion 15 fastened to the face board, anarm portion 16 disposedat right angles to the stem portion 15 and provided with a fingerportion 17 in Contact with the upper edge 18 of rim.l0. Arm portions 16are held in engagement with the rim 10 and the stem portion 15 byfastening means 19 passing through arm portion 16 and secured to theface board 12.

A hub 20 is also removably mounted on the face board 12 and disposed atthe center of the rim. Fastener 21 passing through the hub 20 is securedto the face board 12 and maintains the hub in position on the jig. Aplurality of hollow, thinwalled, thermally crystallizable glass tubes 22are then closely packed together with the rim in parallel ralatio nshipas illustrated in FIG. 1, i.e., the tubes are parallel to the inner wall23 .readily achieved. However, the method of sealing the tubes is not 'apart of this invention, and any of the known methods may be used.

Because it is often desirable and important to have the glass tubes 11as closely packed as possible so that each tube is in contact with sixother tubes, as shown n Flg. 5, the jig ll is provided with a vibrator13 which, in turn, causes face board 12 and rim to vibrate(by means notshown). This vibration is imparted to the plurality of glass tubes 22and assists in more closely packing the tubes as they are placed on topof the tubes which have already been packed. It is to be understood thatthe rim 21 need not be manually packed, but can be packed by othermethods. In either event, the vibrajig 11 and placed upon a stainlesssteel plate 26 having a silica-alumina (Fiberfrax) cloth 27 on its uppersurface, as shown in FIG. 4. Plate 26 is provided with a plurality ofperforations 28. Another Fiberfrax cloth 29 is placed on the uppersurface of the assembly 25, and a second perforated stainless steelplate 30 is placed thereover. A heavy member 31 is finally placed on topof plate 30, and the entire assembly is then placed in a furnace andsubjected to heat sufficient to soften the glass walls of tubes 22 andcause the walls to bloat or expand due to'the heating of the fluidmedium in each tube so that adjoining, contacting wall surfaces arefused together to form a unitary matrix. It is important to have theends of each of the tubes 22 in assembly 25 sealed during the heatingstep; otherwise the tube walls will collapse rather than expand whensubjected to this heat. Furthermore, to utilize the heating proceduredescribed above with respect to the FIG. 4 assembly, the

length of the tubes should be no longer than the height tween the tubes.

The heating of the thin-walled tubes expands them into close contactwith each other and into theinterstices between tubes to a greater orlesser extent, ideally to an extent to substantially completely fill theinterstices between the tubes and between the-tubes and walls of the rimand hub. In the latter event the resulting tubes become essentiallyhexagonal. The glass tubes are fusingtogether and are also undergoingnucleation during the heat treatment, and heating of the structure iscontinued for a time sufficient to in situ crystallize the glass to anat least partially crystalline material,

commonly referred to as a glass-ceramic. The rim and hub can be formedof a conventional inorganic crystalline oxide ceramic, made by firingand sintering particulate inorganic oxide materials. The rim and hubshould, of course, have an average coefficient of lineal thermalexpansion compatible with that of the low expansion material of thematrix. In a preferred embodiment ofthe invention, the rim and hub arealso formed of a thermally crystallizable glass which has beencrystallized to a glass-ceramic having physical properties, includingthermal expansion and contraction properties, which are close to, andusually the same as, those of the crystalline matrix comprising thefused tubes.

After the assembly 25 has been crystallized, and usually after coolingtoroom temperature, the outer surface portions of the assembly areremoved by sawing with adiamond'saw in the direction indicated by linesA in FIg. 4. An assembly of a predetermined thickness as describedhereinbe'fore, except that the ends are sealed and the cells orpassageways are enclosed. The product so produced has exceptionalbuoyancy for a ceramic product, and can be used as a noninflammabl'e.chemically inert buoyancy material in life rafts, for instance, and forother applicationswhere'buoyancy is desired. Furthermore, the ends ofthe tubes may be opened only on one end'to provide a sound-absorptionmaterial which is fireproof and can be used in soundabsorptionapplications. Furthermore, either material, i.e., the material with oneor both ends sealed, is useful as an extremely lightweightheat-insulation material, especially where chemical durability or fireresistance is desired.

In the method of this embodiment of theinvention, the ends 25 of tubes22 are appropriately sealed, e.g., by means of a flame, either before,after or during the bundling of the tubes. Typically, the tubes aresealed in a gaseous environment, so as to trap the environmental gaswithin each tube at the surrounding ambient pressure. On heating toeffect fusionsealing, the gas within each tube expands so as toprevent-collapse of the tubes. With the thin-walled tubes used in thisinvention, expansion of theentr-apped gas causes the tubes to bloat orexpand. In a preferred embodiment the expansion is effected until thespace betweenadjacent tubes is essentially filled, and when the tubesare bundled so that each tube is in contact with six adjacent tubes,asshown in FIGS, the tubes are reformedinto substantially hexagonal shapeto provide-the matrix structure illustrated in FIG. 6. The tubeexpansion may be stopped short of full hexagonal development, but thewall-to-wall pressure created byev en minimal expansion of the tubes hasbeen foundeffective to form tube to-tube seals which are sufficientlytenacious to knit the entire aggregate into an integral, unitarystructure of good mechanical properties. Conversely, open tubes withoutinternal pressure acting upon each tube will collapse or deform underthe influence of gravity where high temperatures soften the glass enoughto cause tube-to-tube bonding.

Tubing used in practicing the usual embodiments of the method of thisinvention has a maximum inner diameter of up to about 0.1 inch, a wallthickness of 0.001 to 0.015 inch and an inside diameter'to wallthickness of at least 6; substantially lower diameter to wall thicknessratios result in a relative ineffectiveness of the process to urge thetubes into a good fusion bond when using'a temperature schedule which isalso effective to properly nucleate and crystallize the glass tubes to aglass-ceramic during the expanding and fusion heating cycle..ln' a nowpreferred embodiment of the invention the ratio of the inner diameter tothe wall thickness of the thermally crystallizable glass tubes is atleast 7.2; when tubes having such diameter to wall thickness ratio areemployed, the unique structure of the invention is made wherein the openfrontal or cross-sectional area of the resulting matrix structure is atleast 65 percent, and it is usually in fact preferred that the open areabe on the order of at'least percent and up to percent or more.

Usually, round thermally crystallizable glass tubing is used in formingthe matrix structure of the invention. Drawing of round glass tubing tocontrolled dimensions is an old established art in industry.

While the assembled tubes 22 can merely be fusion sealed with veryslight expansion and reformation of the tubes, it is preferred for manyapplications that the tubes be expanded and reformed into substantiallyhexagonal shape during fusion sealing. Greater tube-totube pressure isgenerated causing a more perfect fusion of each tube to the surroundingtubes, and tube-totube contact area increases from essentiallytangential contact with adjacent tubes to essentially full contact, withbonding of the entire periphery of the tubes. Furthermore, as thetriangular space between each set of three adjacent tubes (see FIG. issubstantially eliminated by expansion and reformation, the pressure dropin the finished product across the honeycomb structure is less thanacross one in which tubing is round in the final product. The thinnerthe wall thickness for a given composition and the greater the ratioofthe inner diameter to such a wall thickness, the more readily the tubecan be expanded to a substantially hexagonal tube at a giventemperature.

Well suited for use in the method of this invention are thermallycrystallizable glasses that are convertible by heating to glass-ceramicbodies. As used herein, a glassceramic is an inorganic, essentiallycrystalline oxide ceramic material derived from an amorphous inorganicglass by in situ bulk thermal crystallization.

Prior to thermal in situ bulk crystallization, the thermallycrystallizable glasses can be drawn into tubing using conventionalglass-forming techniques and equipment. After being assembled in themanner shown in FIGS. 1 and 4, the thermally crystallizable glass tubesare subjected to a controlled heat treatment until the tubes have beenexpanded and fusion sealed and crystallization has been effected.

Thermally crystallizable glass compositions and the glass-ceramicsresulting from thermal in situ crystallizationn thereof which are usefulin the method and product ofthis invention are those which have, intheir crystallized state, a coefficient of thermal expansion in therange from l2 to +12 l0 /C over the range 0-300 C. The compositionsusually used are those containing lithia, alumina and silica, togetherwith one or more nucleating agents including TiO ZrO SnO or other knownnucleating agents. In general, such compositions containing in weightpercent about 55 to 75 SiO about to '25 A1 0 and about 2 to 6 Li O,together with about 1.5 to 4 weight percent of nucleating agentsselected from one or more of TiO ZrO and SnO can be employed.Preferably, not more than about 2.5 weight percent Ti0 is usually usedor the crystallization is undesirably rapid to be compatible with thefullest expansion of the tubes in the bloating process. Otheringredients can be present in small amounts, as is understood in theart, such as even as much as 4 or 5 weight percent ZnO, up to as much as3 or 4 weight percent CaO, up to as much as 8 percent .MgO, and up to asmuch as 5 percent BaO, so long as the silica plus alumina plus lithiaand the nucleating agent(s) are at least about 85, usually 90, weightpercent of the total glass and the glass composition will thermallycrystallize to a glass-ceramic having the desired low expansion of -l2to +12 l0 /C. Exemplary compositions which can be used in the process ofthe invention include those compositions disclosed in Netherlandsprinted patent application 6,805,259.

In any event, the thermally crystallizable glass tubings in thelithia-alumina-silica field containing nucleating agents as beforedescribed, are assembled as previously set forth and the constrainedbundles of sealed tubing (containing a heat-expansible fluid) are heatedat any suitable rate that will not thermally shock the tubing up to atemperature range in the maximum nucleating range of the glass. Themaximum nucleation range can be determined for all such glasses by thegeneral method outlined in Smith U.S. Pat. No. 3,380,818 beginning atcolumn 9, line 54. For the process of the present invention wheresealing is to be effected or initiated while nucleation is occurring, itis preferred that the assembled tubes be heated in the range 50F. to250F. above the annealing point for a period of 1 hour or more. Thistime can be extended to 10 to 20 hours, and even longer times are notharmful. During this time of heating in such temperature range,nucleation is effected, as well as fusion aided by pressure exerted byexpansion of the entrapped fluid. Thereafter, the temperature is raisedto ahigher temperature than the first heating range, which highertemperature is at least 200 F. above the annealing point temperature ormay be as high as the final crystallization temperature (usually 1800 to2300 F.). The final crystallization can be effected at any suchtemperature range higher than the nucleation-expansionfusion temperature-(50 to 250 F. above the annealing point temperature) and can be as lowas 200 F. above the annealing point or as high as 2300 F. or as high asthe upper liquidus temperature. If the final crystallization is effectedat temperatures no more than 400 or 500 F. above the annealing point,then the product will not have as high tempera-.

ture stability as is desired for gas turbine use, but the product willbe of the desired'low expansion glassceramic. In any event, in thissecond state of heating further expansion and the beginning ofcrystallization is effected, followed by the completion ofcrystallization on continued heating to a degree such that the matrixmaterial has an expansion in the range from 1 2 to +12 X 10 /C. over therange 0300 C. While the temperature may be raised directly to the finalcrystallization temperature at a furnace heating rate of at least 50 F.per hour, it is usually preferred to allow crystallization to beeffected slowly while further expansion and concomitant fusion are beingeffected by having an intermediate step between the firstnucleation-andfusion temperature range and the final crystallizationtemperature, which range is usually from 200 F. to about 500 F. abovethe annealing point of the original glass. Exemplary holding times inthis intermediate range are from 1 to 8 hours, after which the assemblyis heated up to the final crystallization temperature, usually in therange of from about 1800 to 2300 F. Obviously, no specific heattreatment instructions can be given suitable for all thermallycrystallizable glass compositions. As is well-known, glass-ceramics donot have adequate strength if they are not sufficiently nucleated beforecrystals are allowed to grow appreciably in size, so that routineexperiments known to those skilled in the'art are used to determine whatlength of time is best to obtain an adequate number of crystallizationcenters or nuclei in the glass in the nucleation temperature range of 50to 250F. above the annealing point. Another point that must be kept inmind is that, if'it is an object to obtain appreciable expansion beyondthat necessary to get good fusion between the tubes, in otherwords toget appreciable reshaping of the tubes to fill the interstices betweentubings, one should not raise the temperature too slowly when going fromthe nucleation temperature range to the intermediate range, since arigid crystalline network may begin to set in and to preventfurtherexpansion. We have found some compositions can be heated at arate as low as 50 F. per hour to this intermediate temperature range andstill get sufficient expansion of the tubing effective to form hexagonaltubes (round tubes used in close-packed configuration). On the otherhand, some compositions have been found not to fully expand unless theheating rate from the initial nucleation-fusion temperature range to theintermediate temperature range is on the order of at least 200 F. perhour and preferably at least 300 F. per hour.

The length of time of heating in the final crystallization temperaturerange of 1800 F. to about 2300 F. is from one-half hour to or 6 hours,although longer times are in no way deleterious. After thecrystallization has been completed, the structure can be cooled atfurnace rate or in air because the structure is of such low expansionthat thermal shock will not harm it.

When making a regenerator having a rim or having a rim and a hub, asstated, can be made of a thermally crystallizable glass that is therestraining means in which the tubes are initially packed, and the rimcan be heat-treated concomitantly with the tubes, which seal to the rimduring the process.

If, however, a rim of considerable thickness is desired and rapidheating rates such as 200 or 300 F. per hour are used in the heattreatment of the matrix as just described, the glass of the rim maycrack from thermal shock. ln such case it is possible to preheat treatthe rim to a partially crystallized state until it is a relatively lowexpansion material having an expansion coefficient less than or X lO /C.This can be accomplished by using a suitable nucleation andcrystallization heat treatment where the top crystallization temperatureis on the order of 1450 to 1600 F. and the crystallization is effectedonly long enough to bring the coefficient of expansion down to thedesired range. This partially heat treated rim then can be used as therestraining means without fear of thermal shock. It is also possible touse a fully-heat treated or glassceramic rim or a fully formed and heattreated rim made of a low-expansion sintered ceramic material known inthe art, such as ceramic materials that can be made, for instance, frompowdered petalite by suitable sintering methods known in the art. Whathas been said with respect to the rim also applies to regeneratorshaving a hub of ceramic or glass-ceramic material, as illustrated inFIG. 7.

' After the heat treatment just described, the product may now be cooledand the sealed ends of the tubes cut or ground away to open each tube toatmospheric pres sure. Alternatively, if the intermediate step of heattreating is employed, as is usually the case, the heat treatment can beinterrupted after this intermediate step and cooled somewhat or evencooled to room temperature, and the ends of the tubes cut or ground away"and opened to'atmospheric pressure. Then the assemcan be cooled andopened after this heat treating step,

if desired, and thereafter the assembly reheated and the crystallizationheat treatment schedule completed. As will be understood by thoseskilled in the art, the crystals after the second stage of heattreatment may be in the beta-eucruptite or beta-eucryptite-like state.as is referred to in the referenced Smith US. Pat. No. 3,380,818, andalready be highly crystallized and of a low expansion. The final heattreatment will cause further crystallization and conversion of theeucruptitelike crystals to beta-spodumene or beta-spodumenelikecrystals, as is also described in the cited Smith patent.

While the method of the invention has been described in connection withthe usual and important embodiment which starts with tubing having aninternal diameter of 0.1 inch or less, the process is also applicable tomanufacture of fused matrices of glass-ceramic tubes of larger internaldiameter, so long as the ratio of internal diameter to wall thickness isobserved as previously disclosed. Of course, with larger tubings the surface density attribute of the matrices obtained is diminished. Thus,starting with larger tubings a matrix otherwise like the preferredmatrices of the invention is obtained, but without the high surfacedensity. Thus, starting material tubings can be even as large as l, 2 or3 inches, and the process remains essentially the same; also, the novelmatrices produced are essentially the same as with the smaller tubingsexcept for the surface density. Thus, they have the same high percentageof open frontal area and the other attributes of the matrices withsmaller passageways.

As previously mentioned, the tubes can be assembled in any appropriatefashion. Materials for molds in which the tubes are inserted forrestraint during the heat treatment process need not be glass-ceramic orceramic when the object is to make the matrix and not also toconcomitantly seal the matrix to the rim or mold. However, thecircumferentially supporting mold should be made out of a material whichdoes not crack or deform substantially during the heat treating of theassembly. When the mean effective outside diameter of the tube assemblyis about 6 inches or less, it has been discovered that the support canbe constructed out of any metal or metal alloy, such as stainless steel.To prevent chemical reaction or discoloration of the matrix by the metalwith the tubes at elevated temperatures, e.g., at temperature ofnucleation, crystallization, expansion, and/or fusion, a layer ofsilica-alumina (Fiberfrax 970]) paper may be interposed between themetal case and the assembly of glass tubing. For assembly of diametersgreater than 6 inches, the mold should be constructed of a materialhaving substantially the same coefficient of thermal expansion as thematrix in its heat treated state. Glass-ceramic molds work well. Ofcourse, these glass-ceramic molds can also be used with smallerassemblies. using a mold wherein the glass tubes are not in contact withthe walls of the mold result in the matrix 37 shown in FIG. 11 whichconsists essentially of thefused ceramic tubes, without a rim bondedthereto. The matrix is suitable for use as a gas turbine regenerator. Ifdesired, a central opening can be ground therethrough to form a bearingor the matrix can be formed about a hub, as illustrated in FIGS. 1 and12 where the tubes are bonded to the outer walls of the hub.

The glass-ceramic matrix 38 illustrated in FIG. 12 has a plurality ofrecesses 39 formed in its outer periphery, which recesses are adapted toreceive and engage driving means mounted on a gas turbine engine (notshown) to impart a rotary movement to the regenerator or matrix 38. Therecesses 39 can be formed by cutting the periphery ofa matrix such asthat shown in FIG. 11, or the matrix of FIG. 12 can be formed in aspecial mold.

With unlined thermally crystallizable glass or glassceramic molds, thefused bundle of tubes will be bonded to the mold during the heatingcycle to provide a unitary article including a solid rim. Thus, cellularassembly 25 comprises tubes 22, rim l0, and hub 20, all havingsubstantially the same lineal coefficient of thermal expansion andcontraction. In addition to providing lateral support for the expandedand fused tubes 22, rim is highly useful when the cellular structure orassembly 25 is used as a gas turbine regenerator. Many gas turbineengines are designed for rim drive regenerators. By casting or machiningdrive means or receivers, e.g., gear teeth, cups, etc., into rim 10,cellular structure 25 is adapted for use as a rim-driven regeneratorwheel in turbine engines. FIG. 10 illustrates a regenerator wheel 40wherein the outer periphery of the rim 41 is provided with recesses 42.

In a further embodiment of this invention, the tubes are bundled aboutthe circumference or perimeter of a bushing or bearing or core ofamaterial having substantially the same coefficient of thermal expansionas the tubes. Such core 20 can be solid or hollow and typically ispositioned at the center of the assembly.

A matrix assembly 43 is bonded to a rim 44 and having no core or hub isillustrated in FIG. 9. When the center of the matrix is cored and abearing inserted therein, the assembly can be mounted for rotation in agas turbine engine.

Although FIGS. 1 and 4 illustrate articles with only one rim l0, aseries of one or more concentric rims containing the matrix can be used.Thus, as illustrated in FIG. 7, cellular article or assembly 32 cancomprise hub 33, outer ring or rim 34 and inner ring or rim 35 withcellular matrix 36 comprising a plurality of the elongated glass-ceramictubes which are expanded and fused together into a unitary structuretherebetween. The cellular matrix between the hub and the rings has thecharacteristics previously discussed. Use of these concentric ringsenhances the strength of the overall article and serves to protect thematrix surface against abrasion as it rotates relative to a seal bar.

While the foregoing has emphasized the utility of the structure of thisinvention as a gas turbine regenerator, it is well suited for use inother fields. Thus, the cellular article of the invention can be used asa nozzle for a gas-fired burner, as a grating for an infrared heater, asa filter, as a catalyst support, etc. FIG. 13 shows the matrix 45 of theinvention disposed within the nozzle 46 of a gas burner 47, such as aBunsen burner which burns a mixture of gas and air.

The unique. method of the invention is also applicable to making aunitary foraminous glass-ceramic matrix l0 jacent transverse tube. Sucha structure is illustrated in FIG. 14. When, as preferred, the tubes areessentially fully expanded, each tube wall is a common wall with eachtube adjacent thereto, including those in the same plane and those inadjacent parallel planes; moreover, when fully expanded, the passagewaysformed are essentially in the shape of a parallelogram, usually a squareor a rectangle. FIG. 15 illustrates the tubing layers before assembly,using round tubes, while FIG. 14 shows the matrix with the tubesexpanded to essentially square passageways. In FIG. 15 the tubes are notshown as closed, but as they would appear in cross-section. However,they are of course sealed as before described.

After the heat treatment as before described, the integral productcontaining the rectangular or square passageways is obtained. As in theother embodiment of the invention, the material, left sealed, is alightweight and fire-resistant soundor heat-insulation material and isof course a buoyant material. With the ends of the tubes ground off toopen them, the material is suitable as a low expansion, heatand thermalshock resistant heat exchanger or recuperator. Thus, for instance, hotgas from a gas turbine can be passed through the matrix in onedirection, while cold incoming air can be passed through in thetransverse direction, picking up heat from the hot gas turbinecombustion gases.

When starting with round tubes having a ratio of the inner diameter towall thickness of'at least 6, the open or free cross-sectional orfrontal area of each face of the matrix containing passageways is atleast 32 percent. When starting with round tubes having an innerdiameter to wall thickness ratio of 7.2, the open crosssectional orfrontal area of each face containing openings is at least 36 percent.

For many applications, particularly when the matrix is used as a heateschanger or recuperator, it is preferred that the passageways beessentially fully expanded into the shape of a parallelogram, such as asquare or a rectangular passageway. Obviously, such expansionessentially eliminates the interstices between tubes and thus increasesthe effective heat transfer surface from one layer of tubes orpassageways to the adjacent transverse layer of passageways.

To facilitate the assembling of the tubes 53 into layers 52 so that thelayers may be superimposed one upon another, with the tubes in one layerbeing transverse to the tubes in the adjacent layers, a plurality oftubes 52 of definite length are placed side by side in contact withadjacent tubes to form a ribbon of predetermined length. Whilemaintaining the tubes in this parallel contacting relationship, theupper surface of the layer of tubes is spray-coated with an air-settingbonding composition so that the ribbon of tubes becomes rigid enough tohandle like a thin sheet of plastic material. A flame is applied to eachside of the ribbon and held in contact with the ends of the tubes untilthe ends fuse together, trapping air within the tubes. The ribbon oftubes is then cut-into rectangular sheets and the sheets arranged in themanner illustrated in FIG. 15.

The air-setting bonding composition which can be used is a polyurethane,Coverlac A6210, made by Spraylat Corporation, 1 Park Avenue, New York,although other compositions will be readily understood by the art asaccomplishing the same purpose. For instance, a 2.5 to 3 weight percentsolution of nitrocellulose in amyl acetate can also be used. Thecomposition tubes. which ribbon can be cut to desired lengths andutilized in making the recuperator of the invention. A plurality oftubes 53 previously cut to a specified length are fed into hopper 55 bymeans not shown. Hopper 55 is continuously vibrated by means of vibrator56 in contact therewith, so that the tubes 53 are maintained in parallelrelationship and are deposited individually through opening 57 at thebase of the hopper onto support layer 58 disposed directly below opening57 and continuously moving in a direction away from the hopper 55.Support layer 58, which can be a plastic film, paper such as the thinpaper used in making tea bags, cellophane, or other film material, iscontinuously unwound from roll 59 which is rotatably mounted beneathhopper 55. Support layer 58 passes over and is supported by conveyorbelt 60 continuously moving around support rollers 61,62, with either orboth rollers being drive by means not shown but well understood in theart.

As the individual tubes 53 pass through the bottom of the hopper 55 fromopening 57, they are deposited on support layer 58 and move in thedirection away from the hopper. The rate of movement of support layer 58and the rate of deposit of the tubes 53 thereon are adjusted so that thetubes are deposited and maintained in parallel, contacting relationshipwith adjacent tubes. As the support layer and tubes move away fromhopper 55, the ends 63 ofeach tube pass through oppositely disposedburners 64 mounted on either side of conveyor belt 60, and the burnerflames 65 fuse and close the tubes, trapping the air within the tubes.The flames 65 can be directed so that they do not adversely affect thesupport layer 58 but only impinge on the tube ends 63.

As ribbon 54 of parallel tubes continues along the conveyer after thetubes have their ends closed, a thin layer of air-setting bondingmaterial 66 is sprayed onto the upper surface of the ribbon 54 by meansof nozzle 67 of spray gun 68, which material bonds the tubes together sothat the ribbon of tubes becomes rigid enough to be handled like a thinsheet of plastic material. Alternatively, the layer of tubes can besprayed with the bonding material prior to having their ends sealed byflames 65. The support layer 58 is readily separated from the ribbon 54.The ribbon is then cut into rectangular sheets and arranged in themanner illustrated in FIG. 15 so that alternate sheets or ribbons oftubingare transverse to adjacent sheets or ribbons of tubing.Preferably, the tubes in alternate sheets or layers are at 90 angles. I

In another arrangement, support layer 58 can be of a relatively-thinmaterial, such as tea bag paper,to which is applied a binder or adhesiveprior to the tubes 53 being deposited thereon. The tubes thus adhere tothe support layer and the ribbon of tubes thus formed can be cut to thedesired size and assembled to form a rectangular matrix, such asillustrated in FIG. 15. Again, the paper and binder are ofa compositionwhich permits rapid volatilization upon the application of heat for thebloating and fusing of the tubes, without any deleterious residueremaining. Such paper and binders are known in the art.

A plurality of rectangular matrices 51, each consisting essentially oftubes ofthermally crystallizable glass fused together in a monolithicstructure, are arranged in a mold in such a manner that each matrix isadjacent to and separated from each adjoining matrix by a wedge-shapedmember 69 of crystallizable glass and preferably of the same compositionas that from which the tubes 53 in matrices 51 have been formed. Thewedge-shaped member 69 has each of its outer surfaces 70 taperinginwardly within the structure to substantially a point 71. In therecuperator 72 illustrated in FIG. 16, the inner surfaces 73 of eachrectangular matrix 51 is separated by the extremely narrow edge 74 ofthe wedge member 69. It is preferable that edge 74 be as narrow aspossible so that the inner surface of the recuperator is essentiallydefined by the inner surfaces 73 of the matrices, thus providing amaximum of passage ways for gases to pass to the exterior.

Due to the alternating arrangement of rectangular matrices andwedge-shaped members, an annular structure as shown in FIG. 16 is formedwithin the mold. The assembly is then placed in an appropriate furnaceand heated to the nucleating temperature of the particular thermallycrystallizable glass composition utilized in the structure. Afternucleation is completed the nucleated structure is subjected to thetemperature necessary to at least partially crystallize the glass andform a unitary structure or recuperator wherein the contacting surfacesof the rectangular matrices and wedgeshaped members are firmly bonded-or fused to each other. The heat treatment steps for the nucleation andcrystallization of the recuperator members are those described abovewith respect to the regenerator of the present invention.

An alternate method for making the recuperator would be to thermallycrystallize the individual matrices 51 and wedge-shaped members 69 andthen seal the members together to form the structure of FIG. 16. Athermally crystallizable sealing glass having a coefficient of thermalexpansion which is substantially that of the members being sealed isapplied to all contacting surfaces prior to assembling the members. Theassembled structure is then subjected to the heat necessary tocrystallize the sealing glass and bond the members together.

Because of the arrangement of the tubes 53 in the rectangular matricesin the recuperator 72, a cross flow of gases through the recuperator isachieved. Cool exterior gases, as from a compressor, can pass throughthe open passageways of tubes 53 which are in a direction (indicated byarrows A'in FIG. 16) parallel to the axis of the recuperator, while thehot exhaust gases of a gas turbine engine can flow inwardly (indicatedby 17 18 arrows B) into the center 77 of the recuperator and out throughthose passageways which'are transverse to the I axis of the recuperator.Thus, the cool gases such as air, 286 13f, passing through therecuperator passageways are TiOZ' 1.7 heated by the walls of suchpassageways which are, in 5 turn, heated by the gases passing throughthe passage- 31, 0, :5 ways which are transverse to the former andseparated U Na O 0.4

only by the common wall thickness. K20 02 Seal seatingsurfaces 75,76 areprovided on each side of the recuperator. The recuperator of FIG. 16does [0' not have to be rotated nor does it have to come in contact witha seal bar, thus eliminating the wear which Clrcular tubmg havmg anaverage wan thlckness of 0.001 inch and anaverage' inside diameter of0.0l6 inch was drawn from this thermally crystallizable glass. Theinside diameter to wall ratio was 16.0. The tubing was simultaneouslycut and sealed to 3.75 inch lengths with a gas oxygen flame in ambientair. The annealing point of this glass was about 1260F.

The sealed tubing was tightly packed parallel to the normally occurs onthe surfaces of the recuperator formed by the ends of the tubes.

The recuperator of the invention has many advanl5 tages over the metalor ceramic recuperators of the prior art. Metal recuperators haveusually been made of nickel alloy which is expensive and difficult toshape and braze. Such recuperators often leak after repeated cyclings.Recuperators have also been made of corru- 2O gated sheets of ceramicwhich are stacked together to form a cross-flow pattern and thensintered. However, it is difficult to make the joints of these prior artrecuperators and failure of recuperators usually occurs in these areas.Further, heat-resistant metals are expensive and often fail in thermalfatigue while sintered ceramic recuperators are porous. Applicantsrecuperator, on the other hand, is nonporous, has a low expan-Temperature Time or Rate an inside diameter of 4.25 inches. The mold hadpreviously been lined with a layer of 0.125 inch thick alumina-silicapaper (970-1 Fiberfrax). The ends of the mold were then lined with thissame alumina-silica paper and the assemblage heated in an electric kilnon the following schedule:

length of a 3.75 inch thickstainless steel mold having sion coefficientand preferably has a zero-expansion,

and is not subject to thermal fatigue or to weaknesses 0 Q${ %9 I v 396i m: at the JOlflllS. 800 F. to 1350 F. 3662mm. Hold at 1350 F. I 2 Ahrs.

The following examples will serve to illustrate the m- I to 1 3420mmvention without in any way limiting it, since modifica-, Hold at 1750 F0 s. tions will be readily apparent to those having ordinary 1750F/hrskill in the art. All of the matrices made in such examples had theproperties set forth herein including the After this heat tre tment, thees lti 1 -ceramic preferred 65 percent or higher open frontal area. a ru ng g ass matrix was removed from the cylinder, the ends opened EXAMPLEI by grinding, and the product heated at a rate of 50 F./hr to atemperature of 2000 F. and held at that tem- 40 perature for one hour.Then the matrix was cooled to room temperature at a rateof about 51F./hr. The higher temperature heat treatment serves mainly to increasethe stability of the glass-ceramic at operating temperatures asdiscussed hereinbefore.

The foregoing heat treatment thermally in srtu crys- Pans by tallizedthe glass and produced a glass-ceramic matrix. lngrcdicnts Weight Theheat treatment had fusion bonded the walls of each tube to those ofadjacent tubes and reformed each tube The following batch materials,expressed in parts by weight, were melted at a glass temperature of2900F. for about 72 hours in a high alumina refractory (Monol'rax M)tank furnace using a slight excess of air for an oxidizing atmosphere:

0 o .1 r 242.0 izix i [K a xiii 83,5 to substant ally hexagonal shape.The open frontal area Lithium Fluorlde g of the matrix was measured tobe over 76%, and the cofl 25212 efficient of lineal thermal expansionwas about 0.2 X Lithium Carbonate 26.1 lO /C. (0300C.). Measurement offrontal open area was effected by measuring the weight of a specific TiO10.9 volume and comparing it to the density of the solid Zinc Oxide 10.5Zinc Zirconium Silicate 18.2 glass Ceramlc' 99.49? Al O 0.04% F3 0;0135? SiO. 0.13% M 0. 0.3% ignition loss. '-"Si0., 77.28; M20 16.43;[J20 3.90; Na. -O 073; K20 0.42; Fe:O=,0.0 'l3: ignition A heatregenera'tor Similar to that illustrated in FIG loss (LJU.

Si(). .25.-l;ZnO 2).-l'.ZrO. .-15.3. 4 was made in accordance with thefollowing procedure: I. 99.4% Al. .O 0.04% F6203, 0.13% SiO 0.13% A rimhaving a 28 inch diameter and a hub having a N320. 0.3% ignition loss. 3inch diameter were cast slightly oversize in metal 2. Si() 77.28; M 0[6.43; Li O 3.90; Na- O 0.73; moldsusing the thermally crystallizableglass composi- K,() 0.42; F0 0;, 0.033; ignition loss 0.90. 6% tions asdescribed in Example I. The rim and hub were 3. SiO 25.4; ZnO 29.4; Zr045.3. then diamond ground to the 28 inch and 3 inch diame- 'l'hcanalyzed composition of the glass, in weight perters, respectively. andalso ground to a 3.75 inch cent. was as follows: height.

19 Both rim and'hub were prefired in accordance with the following heatschedule after being heated to a temperature of l2 00 F.:

The rim and hub were then mounted on a jig and sealed glass tubinghaving a length of 3.75 inches, an outer diameter of 0.028 inch, and anaverage wall thicknessof 0.0025 inch was packed tightly between the huband rim. The tubing was of the same glass composition as in Example I.The packed assembly was placed horizontally onto an alumina-silica cloth(Fiberfrax) spread over a perforated stainless steel plate. A secondalumina-silica cloth was placed over the assembly, and a secondperforated stainless steel plate placed thereon, in the manner shown inFIG. 4. A weight was placed onto the second steel plate, and the entireassembly was placed into a gas-fired kiln and heated in accordance withthe following schedule:

During this heat treatment, the thermally crystallizable glass tubeswere thermally in situ crystallized to a glass ceramic. They had alsoreformed into generally hexagonal shapes while becoming firmlyfusion-sealed to each other as well as to the rim and the hub. The openfrontal area was about 70 percent.

The outer surfaces of both sides of the assembly were then ground,opening the tubes at either end and establishing the final thickness ofthe assembly. The outer diameter of the-rim was ground to apredetermined size, and drive slates were ground into the solid rimabout its circumference. A center bearing hole was bored through the huband the walls of the hole were ground to a predetermined size.

The coefficient of lineal thermal expansion of the assembly wasmeasured, and the results were as follows:

EXAMPLE Ill Usingthe thermally crystallizable glass composition ofExample I, circular tubing having a wall thickness of 0.003 inch and anaverage inside diameter of 0.028 inch was drawn and sealed in 3.75 inchlengths as in Example l. After packing the sealed tubing in a stainlesssteel mold, as in Example I, the assembly was heated in an electric kilnaccording to the following schedule:

Temperature Time or Rate Ambient to 800 F. 396F./nr. Hold 800 F. 1 hr.800 F. to 1350 F. 366F./hr. Hold 1350 F. 2% hrs. l350 F. to 1750 F.300F./hr. Hold 1750 F. 10 hrs. l750 F. to 2000 F. 50F./hr. Hold 2000 F.10 mins.

2000 F. to F.

After removal from the stainless steel cylinder, the ends of theresulting matrix were ground open with a diamond abrasivewheel. None ofthe individual tubes had collapsed during the heating cycle, and thetubes making up the matrix, still substantially circular incross-section, were well bonded to each other.

During the heat treatment, the glass had converted to a glass-ceramic bythermal in situcrystallization. By

testing samples of the samecomposition which had been subjected to thesame heat treatment, it was found that the walls of the tubes had acoefficient of lineal thermal expansion of 0.2 X 10 /C. over the rangeof 0 to 300 C., and an average thermal-conductivity of 0.0035cal/cm/sec/C./cm measured using a hot side of 648C. and a cold side of88C. The matrix had an open frontal area of about 71 percent.

EXAMPLE lV Glass tubing was drawn to an average outside diameter of0.050 inch, inside diameter of. 0.046 inch, and a 0.002 inch wallthickness by the following procedure:.

The glass wasmelted and held at 2900 F. in a gas fired furnace for 24hours. The temperature was then lowered to 2475 F., and drawing of thetubing, averaging three-eighth -inch outside diameter, was begun. Thistubing was subsequently reheated to 1600 F. at one end and drawn down tothe aforementioned size.

The tubing glass had the following composition:

Component Weight Percent SiO A1 0 Ti0 ZrO 2 3 CaO MgO Li O Na O K 0 ltsannealing point temperature was about 1250 F.

The tubing was cut and sealed at both ends by a flame into 4-inchlengths, and the tubing was then closely packed into a larger tube ofthe same composition having a seven-eighth-inch inside diameter of a1-inch outside diameter and having a length of 4 inches.

The assembly was heated from room temperature to 1,925F. at a rate of350 F/hr, held at that temperature for one hour, and then cooled to roomtemperature at the rate of 350F./hr. The ends of the assembly were thencut off.. Because ofthe internal air pressure developed in the tubesduring firing, the tubes had expanded and bonded to each other and tothe walls of the larger tubing that served to restrain the expandingbundles of sealed tubes.

To fully crystallize the assembly, it was heat treated according to thefollowing schedule:

The thermally crystallized matrix assembly was cut into sections ofthree-eighth inch thickness with a diamond saw and used as burner grids.A gas-air mixture was fed through a burner terminating with one of thehonecomb sections. The burning fuel mixture quickly heated the glassceramic grid to incandescence, and-the incandescent surface then servedas a catalytic surface to promote the gas-air reaction. The result was asteady, efficient radiant flame.

Specimens of the same glass-ceramic were measured for various physicalproperties. The intrinsic density of the material was found to be 2.5g/cc; the bulk density of the expanded matrix was 0.39 g/cc; and thecoefficient of lineal thermal expansion was 8 X l /C. (0300C.). The openfrontal area was measured to be about 85 percent.

As used herein in the claims appended hereto, the

term glass-ceramic" is an inorganic crystalline oxide ceramic materialcontaining a multiplicity of extremely small inorganic oxide crystals inrandom orientation throughout the mass of the material, whichglassceramic is formed by the thermal in situ bulk crystallization of aglass.

While there have-been shown and described and pointed out thefundamental novel features of the invention with a reference topreferred embodiments thereof, those skilled in the art will recognizethe various changes, substitutions, omissions, and modifications in thestructure illustrated may be made by those skilled in the art withoutdeparting from the spirit of the invention.

What is claimed is:

l. A method for making a glass-ceramic matrix comprising an assembly ofintegrally fused tubes forming a series of smooth, longitudinal parallelpassageways therethrough, wherein the walls defining said passagewayshave essentially zero proosity and an average coefficient of linealthermal expansion of about -12 to +12 X l0 /C. over the range 0300C.,which comprises l. tightly packing together a multiplicity of elongatedtubes made ofa glass that is thermally crystallizable to a low expansionglass-ceramic having a coefficient of lineal thermal expansion of about12 to +l2 l0 /C. over the range before stated, each of the tubes beingsealed at each end and containing an expansible, fluid medium, each ofsaid tubes being essentially parallel to the other tubes in the pack,

2. said tubes having a maximum inner diameter of O. l inch, a wallthickness of about 0.015 inch to about 0.001 inch and an inner diameterto wall thickness ratio of at least 6,

3. constraining the outer periphery of said tightly packed tubes againstoutward movement in a direction perpendicular to said longitudinalpassageways,

4. subjecting said constrained tightly packed tubes to a temperaturesufficient to soften said tubes and thus to cause said fluid mediumentrapped therein to urge the said tubes into tight contact withadjacent tubes, thereby to aid in the fusion of such tubes, saidtemperature being in the temperature range of to 250 F. above theannealing point of said glass, in which temperature range said glassnucleates during said expansion and fusion, and

5. thereafter further heating said tubes to a higher temperature thanthe temperature in step '4 in the range from 200 to 500 F. above theannealing 7 point of the original glass, and

6 finally heating said fused matrix in a temperature range of from l800to 2300 F. and thereby completing crystallization thereof to aglass-ceramic having an expansion in the range aforementioned. 2. Themethod as definedin claim 1 wherein said tubes are tightly packed withinan inorganic crystalline oxide ceramic rim and are constrained fromoutward movement by said rim, the tubes adjacent said rim fusion-bondingto said rim during said heat treatment steps, said rim having acoefficient of thermal expansion substantially the same as that of saidexpanded and fused glass-ceramic tubes. 1

3. The method as defined in claim 2 wherein said 7 'tubes are tightlypacked about an inorganic crystalline oxide ceramic hub disposedcentrally of saidpacked tubes, the tubes adjacent to said hubfusion-bonding to said hub during said heat treatment steps, said hubhaving a coefficient of thermal expansion substantially the same as thatof said expanded and fused glass-ceramic tubes.

4. The method as defined in claim 3 wherein said thermallycrystallizable glass tubes have a wall thickness sufficient to permitsubstantially complete expansion of said glass tubes by the fluid mediumtherein during the aforementioned heat treatment step, said expandedtubes being substantially-hexagonal in crosssection and substantiallyall of the interstices between said tubes being occupied by theexpandedportions of the tubes. I

5. A method according to claim 1 wherein said ratio of inner diameter towall thickness is at least 7.2.

6. A process according to claim 1 wherein the assembly of integrallyfused tubes is partially crystallized to a low expansion in the heattreatment step before step (6) and then cooled and the sealed ends ofthe tubes opened, before reheating and effecting the heating andfinalcrystallization step (6) recited in said claim 1.

7. A method for making a glass-ceramic matrix comprising an assembly ofintegrally fused tubes forming a series of smooth, longitudinal parallelpassageways therethrough, wherein the walls defining said passagewayshave essentially zero porosity and an average coefficient of linealthermal expansion of about '12 to +12 X 10 /C., over the range 0-300C.,which comprises l. tightly packing together a multiplicity of elongatedtubes made of a glass that is thermally crystallizable to a lowexpansion glass-ceramic having a coefficient of lineal thermal expansionof about -l2 to +12 X l" /C. over the range before stated, each of thetubes being sealed at each end and containing an expansible, fluidmedium, each of said tubes being essentially parallel to the other tubesin the pack,

2. said tubes having a ratio of inner diameter to wall thickness of atleast 6,

3. constraining the outer periphery of said tightly packed tubes againstoutward movement in a direction perpendicular to said longitudinalpassageways,

4. subjecting said constrained tightly packed tubes to a temperaturesufficient to soften said tubes and thus to cause said fluid mediumentrapped therein to urge the said tubes into tight contact withadjacent tubes, thereby to aid in the fusion of such tubes, saidtemperature being in the temperature range of 50 to 250 F. above theannealing point of said glass. in which temperature range said glassnucleates during said expansion and fusion, and

thereafter further heating said tubes to a higher temperature than thetemperature in step 4 in the range from 200 to 500 F. above theannealing point of the original glass, and

6. finally heating said fused matrix in a temperature range of from l800to 2300 F. and thereby completing crystallization thereof to aglass-ceramic having an expansion in the range aforementioned.

8. The method for making a matrix as defined in claim 7 including thestep of opening the sealed ends of the tubes in said assembly of fusedtubes after said tubes have expanded and prior to continuing with thenext heat treatment step.

9. The process according to claim 7 wherein the assembly of integrallyfused tubes is partially crystallized to a low expansion in the heattreatment step before step (6) and then cooled and the sealed ends ofthe tubes opened, before reheating and effecting the heating and finalcrystallization step (6) recited in claim 7.

10. The method as defined in claim 7 wherein said thermallycrystallizable glass tubes have a wall thickness sufficient to permitsubstantially complete expansion of said glass tubes by the fluid mediumtherein during the aforementioned heat treatment step, said expandedtubes being substantially hexagonal in crosssection and substantiallyall of the interstices between said tubes being occupied by the expandedportions of the tubes.

11. A method for making a glass-ceramic matrix comprising an assembly ofintegrally fused tubes forming a series of smooth, longitudinal parallelpassageways therethrough, wherein the walls defining said passagewayshave essentially zero porosity and an average coefficient of linealthermal expansion of about l2 to +1 2 X l0 /C., over the range 0300.C.,which comprises l. tightly packing together a multiplicity of elongatedtubes made ofa glass that is thermally crystallizable to a low expansionglass-ceramic having a coefficient of lineal thermal expansion of about-l2 to +l2 X l0' /C. over the range before stated, each of the tubesbeing sealed at each end and containing an expansible, fluid medium,each of said tubes being essentially parallel to the other tubes in thepack,

2. said tubes having a maximum inner diameter of 0. 1 inch, a wallthickness of about 0.015 inch to about 0.00l inch and an inner diameterto wall thickness ratio of at least 6,

3. constraining the outer periphery of said tightly packed tubes againstoutward movement in a direction perpendicular to said longitudinalpassageways,

4. subjecting said constrained tightly packed tubes to a temperaturesufficient to soften said tubes and thus to cause said fluid mediumentrapped therein to urge the said tubes into tight contact withadjacent tubes, thereby to aid in the fusion of such tubes, saidtemperature being in the temperature range of to 250 F. above theannealing point of said glass, in which temperature range said glassnucleates during said expansion and fusion, and

5. thereafter further heating said tubes at a rate of at least 50 F. perhour to a higher temperaturethan the temperature in step 4 and at least200 F. above the annealing point temperature of the original glass andheat treating the matrix of tubes and thus effecting further expansionand crystallization, and continuing suchheating until a sealedglassceramic matrix having a linear expansion coefficient in the rangefrom l2 to +12 X l0 /C. over the range 0300C. is obtained.

12. A method for making a glass-ceramic matrix comprising an assembly ofintegrally fused tubes forming a series of smooth, longitudinal parallelpassageways therethrough, wherein the walls defining said passagewayshave essentially zero porosity and an average coefficient of linealthermal expansion of about l 2 to +12 X l0 /C., over the range 0300C.,which comprises l. tightly packing together a multiplicity of elongatedtubes made ofa glass that is thermally crystallizable to a low expansionglass-ceramic having a coefficient of lineal thermal expansion ofaboutl2 to +12 X l0 /C. over the range before stated, each of the tubes beingsealed at each end and containing an expansible, fluid medium, each ofsaid tubes being essentially parallelto the other tubes in the pack,

2. said tubes having a ratio of inner diameter to wall thickness of atleast 6,

3. constraining the outer periphery of said tightly packed tubes againstoutward movement in a direction perpendicular to said longitudinalpassageways,

4. subjecting said constrained tightly packed tubes to a temperaturesufficient to soften said tubes and thus to cause said fluid mediumentrapped therein to urge the said tubes into tight contact withadjacent tubes, thereby to aid in the fusion of such tubes, saidtemperature being in the temperature range of 50 to 250 F. above theannealing point of said glass, in which temperature range said glassnucleates during said expansion and fusion, and 5.thereafter furtherheating said tubes at a rate of at least 50 F. per hour to a highertemperature than the temperature in step 4 and at least 200 F. above theannealing point temperature of the original glass, and heat treating thematrix of tubes and thus effecting further expansion andcrystallization, and

continuing such heating until a sealed glassceramic matrix having alinear expansion coefficient in the range from 12 to +12 X 10 /C. overthe range -300 C. is obtained.

13. A method for making a glass-ceramic matrix comprising an assembly ofintegrally fused tubes forming a series of smooth, longitudinal parallelpassageways therethrough, wherein the walls defining said passagewayshave essentially zero porosity and an average coefficient of linealthermal expansion of about l2 to +12 X l0 /C., over the range 0 3000C.,which comprises 1. tightly packing together a multiplicity of elongatedtubes made of a glass that is thermally crystallizable to a lowexpansion glass-ceramic having a coeffi-. cient of lineal thermalexpansion of about 12 to +12 /C. over the range before stated, each ofthe tubes being sealed at each end and containing anexpansible, fluidmedium, each of said tubes being essentially parallel to the other tubesin the pack,

2. said tubes having a ratio of inner diameter to wall thickness of atleast 6,

'3. constraining the outer periphery of said tightly packed tubesagainst outward movement in a direction perpendicular to saidlongitudinal passageways,

4. subjecting said constrained tightly packed tubes to a temperaturesufficient to soften said tubes and thus to cause said fluid mediumentrapped therein to urge the said tubes into tight contact withadjacent tubes, thereby to aid in the fusion of such tubes, saidtemperature being in the temperature range of 50 to 250 F. above theannealing point of said glass, in which temperature range said glassnucleates during said expansion and fusion, thereafter further heatingsaid matrix of fused tubes to a higher temperature than the temperaturein step (4) but in the range 200 to 500 above the annealing pointtemperature of the original glass, and thereby heat treating the matrixof tubes in said temperature range and thus effecting further expansionand crystallization to a low coefficient of expansion, 6. cooling thematrix and opening the ends of the tubes to the atmosphere, and 7.thereafter reheating the opened matrix of tubes to a higher temperaturerange that that in step (5) and continuing such heating in such highertemperature range until a fused glass-ceramic matrix having a linearexpansion coefficient in the range from l2 to +12 X l0 /C. over therange O-300 C. is obtained. 14. A method for making a regeneratorcomprising a glass-ceramic matrix comprising an assembly of integrallyfused tubes forming a series of smooth, longitudinal parallelpassageways therethrough, wherein the walls defining said passagewayshave essentially zero porosity and an average coefficient of linealthermal expansion of about l2 to +12 X l0 /C over the range 0-300C,which comprises I 1. tightly packing together a multiplicity ofelongated tubes made ofa glass that is thermally crystallizable to a lowexpansion glass-ceramic having a coeffiing anexpansible, fluid medium,each of said tubes being essentially parallel to the other tubes in thepack, v

' 2. said tubes having a ratio of inner diameter to wall thickness ofatleast 6,

3. constraining the outer periphery of said tightly packed tubes againstoutward movement in a direction perpendicular to said longitudinalpassageways,

4. subjecting said constrained tightly packed tubes to a temperaturesufficient to soften said tubes and thus to cause said fluid mediumentrapped therein to urge the said tubes into tight contact withadjacent tubes, thereby to aid in the fusion of such tubes, saidtemperature being in the temperature range of 50 to 250F above theannealing point of said glass, in which temperature range said glassnucleates during said expansion and fusion, and

5. thereafter further heating said tubes to a higher temperature thanthe temperature in step 4 in the range from 200 to 500F above theannealing point of the original glass, and

6. finally heating said fused matrix in a temperature range of from 1800to 2300F and thereby completing crystallization thereof to aglass-ceramic having an expansion in the range aforementioned.

15. The method for making a regenerator as defined in claim 14includingthe step of opening the sealed ends of the tubes in saidassembly of fused tubes after said tubes have expanded and prior tocontinuing with the next heat treatment step.

16. The process-according to claim 14 wherein assembly of integrallyfused tubes is partially crystallized to a low expansion in the heattreatment step before step (6) and then cooled and the sealed ends ofthe tubes opened, before reheating and effecting the heating and finalcrystallization step (6) recited in claim 14.

17. The process according to claim 14 wherein said glass tubes have amaximum inner diameter of0.1 inch, and a wall thickness of about 0.015inch to about 0.001 inch.

18. A method for making a regenerator comprising a glass-ceramic matrixcomprising an assembly of integrally fused tubes forming a series ofsmooth, longitudinal parallel passageways therethrough, wherein the.walls defining said passageways have essentially zero porosity and anaverage coefficient of lineal thermal expansion of about 12 to +12 X 10'/C, over the range of 0300C, which comprises 1. tightly packing togethera multiplicity of elongated tubes made of a glass that is thermallycrystallizable to a low expansion glass-ceramic having a coefficient oflineal thermal expansion of about 12 to +12 X l0 /C over the rangebefore stated, each of the tubes being sealed at each end and containingan expansible, fluid medium, each of said tubes being essentiallyparallel to the other tubes in the pack, 2. said tubes having a ratio ofinner diameter to wall thickness of at least 6,

' 3. constraining the outer periphery of said tightly packed tubesagainst outward movement in a direction perpendicular to saidlongitudinal passageways,

4. subjecting said constrained tightly packed tubes to a temperaturesufficient to soften said tubes and thus to cause said fluid mediumentrapped therein to urge the said tubes. into tight contact withadjacent tubes, thereby to aid in the fusion of such tubes, saidtemperature being in the temperature range of 50 to 250F above theannealing point of said glass, in which temperature range said glassnucleates during said expansionand fusion,

5. thereafter further heating said matrix of fused tubes to a highertemperature than the temperature in step (4) but inthe range 200 to 500above the annealing point temperature of the original glass, and therebyheat treating the matrix of tubes in said temperature range and thuseffecting further expansison and crystallization to a low coefficient ofexpansion,

6. cooling the matrix and opening the ends of the tubes to theatmosphere, and

7. thereafter reheating the opened matrix of tubes to a highertemperature range than that in step (5) and continuing such heating insuch higher temperature range until a fused glass-ceramic matrix havinga linear expansion coefficient in the range from -12 to +12 X /C overthe range 0-300C is obtained.

19. A method for making a glass-ceramic matrix comprising an assembly ofintegrally fused tubes forming a series of smooth, longitudinal parallelpassageways therethrough, wherein the walls defining said passagewayshave essentially zero porosity and an average coefficient of linealthermal expansion of about l2 to +12 X l0' /C over the range of 0300C,which comprises l. tightly packing together a multiplicity of elongatedtubes made of a glass that is thermally crystallizable to a lowexpansion glass-ceramic having a coefficient of lineal thermal expansionof about .---12 to +12 X 10 /C over the range before stated, each of thetubes being sealed at each end and containing an expansible, fluidmedium, each of said tubes being essentially parallel to the other tubesin the pack,

2. said tubes having a ratio of inner diameter to wall thickness of atleast 6,

3. constraining the outer periphery of said tightly packed tubes againstoutward movement in a direction perpendicular to said longitudinalpassageways,

4. subjecting said constrained tightly packed tubes to a temperaturesufficient to soften said tubes and thus to cause said fluid mediumentrapped therein to urge the said tubes into tight contact withadjacent tubes, thereby to aid in the fusion of said tubes, saidtemperature being in the temperature range of 50 to 250F above theannealing point of said glass, in which temperature range said glassnucleates during said expansion and fusion, and

i 5. thereafter further heating said tubes to a higher temperature thanthe temperature in step 4 and at least 200F above the annealing pointtemperature of the original glass, and heat treating the matrix of tubesand thus effecting further expansion and crystallization, and continuingsuch heating until a sealed glass-ceramic matrix having a linearexpansion coefficient in the range from -12 to +12 X 1O /C over therange 0-300C is obtained.

1. TIGHTLY PACKING TOGETHER A MULTIPLICITY OF ELONGATED TUBES MADE OF AGLASS THAT IS THERMALLY CRYSTALLIZABLE TO A LOW EXPANSION GLASS-CERAMICHAVING A COEFFICIENT OF LINEAL THERMAL EXPANSION OF ABOUT -12 TO +12 X10+**7/*C. OVER THE RANGE BEFORE STATED, EACH OF THE TUBES BEING SEALEDAT EACH END AND CONTAINING AN EXPANSIBLE, FLUID MEDIUM, EACH OF SAIDTUBES BEING ESSENTIALLY PARALLEL TO THE OTHER TUBES IN THE PACK,
 1. AMETHOD FOR MAKING A GLASS-CERAMIC MATRIX COMPRISING AN ASSEMBLY OFINTEGRALLY FUSED TUBES FORMING A SERIES OF SMOOTH, LONGITUDINAL PARALLELPASSAGEWAYS THERETHROUGH, WHEREIN THE WALLS DEFINING SAID PASSAGEWAYSHAVE ESSENTIALLY ZERO PROOSITY AND AN AVERAGE COEFFICIENT OF LINEALTHERMAL EXPANSION OF ABOUT -12 TO +12 X 10**-7/*C. OVER THE RANGE0*-300*C., WHICH COMPRISES
 2. SAID TUBES HAVING A MAXIMUM INNER DIAMETEROF 0.1 INCH, A WALL THICKNESS OF ABOUT 0.015 INCH TO ABOUT 0.001 INCHAND AN INNER DIAMETER TO WALL THICKNESS RATIO OF AT LEAST 6,
 2. Themethod as defined in claim 1 wherein said tubes are tightly packedwithin an inorganic crystalline oxide ceramic rim and are constrainedfrom outward movement by said rim, the tubes adjacent said rimfusion-bonding to said rim during said heat treatment steps, said rimhaving a coefficient of thermal expansion substantially the same as thatof said expanded and fused glass-ceramic tubes.
 2. said tubes having amaximum inner diameter of 0.1 inch, a wall thickness of about 0.015 inchto about 0.001 inch and an inner diameter to wall thickness ratio of atleast 6,
 2. said tubes having a maximum inner diameter of 0.1 inch, awall thickness of about 0.015 inch to about 0.001 inch and an innerdiameter to wall thickness ratio of at least 6,
 2. said tubes having aratio of inner diameter to wall thickness of at least 6,
 2. said tubeshaving a ratio of inner diameter to wall thickness of at least 6, 2.said tubes having a ratio of inner diameter to wall thickness of atleast 6,
 2. said tubes having a ratio of inner diameter to wallthickness of at least 6,
 2. said tubes having a ratio of inner diameterto wall thickness of at least 6,
 2. said tubes having a ratio of innerdiameter to wall thickness of at least 6,
 3. constraining the outerperiphery of said tightly packed tubes against outward movement in adirection perpendicular to said longitudinal passageways, 3.constraining the outer periphery of said tightly packed tubes againstoutward movement in a direction perpendicular to said longitudinalpassageways,
 3. constraining the outer periphery of said tightly packedtubes against outward movement in a direction perpendicular to saidlongitudinal passageways,
 3. constraining the outer periphery of saidtightly packed tubes against outward movement in a directionperpendicular to said longitudinal passageways,
 3. constraining theouter periphery of said tightly packed tubes against outward movement ina direction perpendicular to said longitudinal passageways, 3.constraining the outer periphery of said tightly packed tubes againstoutward movement in a direction perpendicular to said longitudinalpassageways,
 3. constraining the outer periphery of said tightly packedtubes against outward movement in a direction perpendicular to saidlongitudinal passageways,
 3. constraining the outer periphery of saidtightly packed tubes against outward movement in a directionperpendicular to said longitudinal passageways,
 3. The method as definedin claim 2 wherein said tubes are tightly packed about an inorganiccrystalline oxide ceramic hub disposed centrally of said packed tubes,the tubes adjacent to said hub fusion-bonding to said hub during saidheat treatment steps, said hub having a coefficient of thermal expansionsubstantially the same as that of said expanded and fused glass-ceramictubes.
 3. CONSTRAINING THE OUTER PERIPHERY OF SAID TIGHTLY PACKED TUBESAGAINST OUTWARD MOVEMENT IN A DIRECTION PERPENDICULAR TO SAIDLONGITUDINAL PASSAGEWAYS,
 4. SUBJECTING SAID CONSTRAINED TIGHTLY PACKEDTUBES TO A TEMPERATURE SUFFICIENT TO SOFTEN SAID TUBES AND THUS TO CAUSESAID FLUID MEDIUM ENTRAPPED THEREIN TO URGE THE SAID TUBES INTO TIGHTCONTACT WITH ADJACENT TUBES, THEREBY TO AID IN THE FUSION OF SUCH TUBES,SAID TEMPERATURE BEING IN THE TEMPERATURE RANGE OF 50* TO 250*F. ABOVETHE ANNEALING POINT OF SAID GLASS, IN WHICH TEMPERATURE RANGE SAID GLASSNUCLEATES DURING SAID EXPANSION AND FUSION, AND
 4. subjecting saidconstrained tightly packed tubes to a temperature sufficient to softensaid tubes and thus to cause said fluid medium entrapped therein to urgethe said tubes into tight contact with adjacent tubes, thereby to aid inthe fusion of such tubes, said temperature being in the temperaturerange of 50* to 250* F. above the annealing point of said glass, inwhich temperature range said glass nucleates during said expansion andfusioN, and
 4. subjecting said constrained tightly packed tubes to atemperature sufficient to soften said tubes and thus to cause said fluidmedium entrapped therein to urge the said tubes into tight contact withadjacent tubes, thereby to aid in the fusion of such tubes, saidtemperature being in the temperature range of 50* to 250*F above theannealing point of said glass, in which temperature range said glassnucleates during said expansion and fusion, and
 4. subjecting saidconstrained tightly packed tubes to a temperature sufficient to softensaid tubes and thus to cause said fluid medium entrapped therein to urgethe said tubes into tight contact with adjacent tubes, thereby to aid inthe fusion of such tubes, said temperature being in the temperaturerange of 50* to 250* F. above the annealing point of said glass, inwhich temperature range said glass nucleates during said expansion andfusion, and 5.thereafter further heating said tubes at a rate of atleast 50* F. per hour to a higher temperature than the temperature instep 4 and at least 200* F. above the annealing point temperature of theoriginal glass, and heat treating the matrix of tubes and thus effectingfurther expansion and crystallization, and continuing such heating untila sealed glass-ceramic matrix having a linear expansion coefficient inthe range from -12 to +12 X 10 7/*C. over the range 0*-300* C. isobtained.
 4. subjecting said constrained tightly packed tubes to atemperature sufficient to soften said tubes and thus to cause said fluidmedium entrapped therein to urge the said tubes into tight contact withadjacent tubes, thereby to aid in the fusion of such tubes, saidtemperature being in the temperature range of 50* to 250* F. above theannealing point of said glass, in which temperature range said glassnucleates during said expansion and fusion,
 4. subjecting saidconstrained tightly packed tubes to a temperature sufficient to softensaid tubes and thus to cause said fluid medium entrapped therein to urgethe said tubes into tight contact with adjacent tubes, thereby to aid inthe fusion of such tubes, said temperature being in the temperaturerange of 50* to 250* F. above the annealing point of said glass, inwhich temperature range said glass nucleates during said expansion andfusion, and
 4. subjecting said constrained tightly packed tubes to atemperature sufficient to soften said tubes and thus to cause said fluidmedium entrapped therein to urge the said tubes into tight contact withadjacent tubes, thereby to aid in the fusion of such tubes, saidtemperature being in the temperature range of 50* to 250* F. above theannealing point of said glass, in which temperature range said glassnucleates during said expansion and fusion, and
 4. subjecting saidconstrained tightly packed tubes to a temperature sufficient to softensaid tubes and thus to cause said fluid medium entrapped therein to urgethe said tubes into tight contact with adjacent tubes, thereby to aid inthe fusion of such tubes, said temperature being in the temperaturerange of 50* to 250*F above the annealing point of said glass, in whichtemperature range said glass nucleates during said expansion and fusion,4. subjecting said constrained tightly packed tubes to a temperaturesufficient to soften said tubes and thus to cause said fluid mediumentrapped therein to urge the said tubes into tight contact withadjacent tubes, thereby to aid in the fusion of said tubes, saidtemperature being in the temperature range of 50* to 250*F above theannealing point of said glass, in which temperature range said glassnucleates during said expansion and fusion, and
 4. The method as definedin claim 3 wherein said thermally crystallizable glass tubes have a wallthickness sufficient to permit substantially complete expansion of saidglass tubes by the fluid medium therein during the aforementioned heattreatment step, said expanded tubes being substantially hexagonal incross-section and substantially all of the interstices between saidtubes being occupied by the expanded portions of the tubes.
 5. A methodaccording to claim 1 wherein said ratio of inner diameter to wallthickness is at least 7.2.
 5. thereafter further heating said tubes to ahigher temperature than the temperature in step 4 and at least 200*Fabove the annealing point temperature of the original glass, and heattreating the matrix of tubes and thus effecting further expansion andcrystallization, and continuing such heating until a sealedglass-ceramic matrix having a linear expansion coefficient in the rangefrom -12 to +12 X 10 7/*C over the range 0*-300*C is obtained. 5.thereafter further heating said matrix of fused tubes to a highertemperature than the temperature in step (4) but in the range 200* to500* above the annealing point temperature of the original glass, andthereby heat treating the matrix of tubes in said temperature range andthus effecting further expansison and crystallization to a lowcoefficient of expansion,
 5. thereafter further heating said tubes at arate of at least 50* F. per hour to a higher temperature than thetemperature in step 4 and at least 200* F. above the annealing pointtemperature of the original glass and heat treating the matrix of tubesand thus effecting further expansion and crystallization, and continuingsuch heating until a sealed glass-ceramic matrix having a linearexpansion coefficient in the range from -12 to +12 X 10 7/*C. over therange 0*-300*C. is obtained.
 5. thereafter further heating said tubes toa higher temperature than the temperature in step 4 in the range from200* to 500* F. above the annealing point of the original glass, and 5.thereafter further heating said matrix of fused tubes to a highertemperature than the temperature in step (4) but in the range 200* to500* above the annealing point temperature of the original glass, andthereby heat treating the matrix of tubes in said temperature range andthus effecting further expansion and crystallization to a lowcoefficient of expansion,
 5. thereafter further heating said tubes to ahigher temperature than the temperature in step 4 in the range from 200*to 500*F above the annealing point of the original glass, and 5.thereafter further heating said tubes to a higher temperature than thetemperature in step 4 in the range from 200* to 500* F. above theannealing point of the original glass, and
 5. THEREAFTER FURGHER HEATINGSAID TUBES TO A HIGHER TEMPERATURE THAN THE TEMPERATURE IN STEP 4 IN THERANGE FROM 200* TO 500*F. ABOVE THE ANNEALING POINT OF THE ORIGINALGLASS, AND
 6. finally heating said fused matrix in a temperature rangeof from 1800* to 2300* F. and thereby completing crystallization thereofto a glass-ceramic having an expansion in the range aforementioned. 6.FINALLY HEATING SAID FUSED MATRIX IN A TEMPERATURE RANGE OF FROM 1800*TO 2300*F. AND THEREBY COMPLETING CRYSTALLIZATION THEREOF TO AGLASS-CERAMIC HAVING AN EXPANSION IN THE RANGE AFOREMENTIONED. 6.finally heating said fused matrix in a temperature range of from 1800*to 2300*F and thereby completing crystallization thereof to aglass-ceramic having an expansion in the range aforementioned. 6.cooling the matrix and opening the ends of the tubes to the atmosphere,and
 6. finally heating said Fused matrix in a temperature range of from1800* to 2300* F. and thereby completing crystallization thereof to aglass-ceramic having an expansion in the range aforementioned. 6.cooling the matrix and opening the ends of the tubes to the atmosphere,and
 6. A process according to claim 1 wherein the assembly of integrallyfused tubes is partially crystallized to a low expansion in the heattreatment step before step (6) and then cooled and the sealed ends ofthe tubes opened, before reheating and effecting the heating andfinalcrystallization step (6) recited in said claim
 1. 7. thereafterreheating the opened matrix of tubes to a higher temperature range thanthat in step (5) and continuing such heating in such higher temperaturerange until a fused glass-ceramic matrix having a linear expansioncoefficient in the range from -12 to +12 X 10 7/*C over the range0*-300*C is obtained.
 7. A method for making a glass-ceramic matrixcomprising an assembly of integrally fused tubes forming a series ofsmooth, longitudinal parallel passageways therethrough, wherein thewalls defining said passageways have essentially zero porosity and anaverage coefficient of lineal thermal expansion of about -12 to +12 X 107/*C., over the range 0*-300*C., which comprises
 7. thereafter reheatingthe opened matrix of tubes to a higher temperature range that that instep (5) and continuing such heating in suCh higher temperature rangeuntil a fused glass-ceramic matrix having a linear expansion coefficientin the range from -12 to +12 X 10 7/*C. over the range 0*-300* C. isobtained.
 8. The method for making a matrix as defined in claim 7including the step of opening the sealed ends of the tubes in saidassembly of fused tubes after said tubes have expanded and prior tocontinuing with the next heat treatment step.
 9. The process accordingto claim 7 wherein the assembly of integrally fused tubes is partiallycrystallized to a low expansion in the heat treatment step before step(6) and then cooled and the sealed ends of the tubes opened, beforereheating and effecting the heating and final crystallization step (6)recited in claim
 7. 10. The method as defined in claim 7 wherein saidthermally crystallizable glass tubes have a wall thickness sufficient topermit substantially complete expansion of said glass tubes by the fluidmedium therein during the aforementioned heat treatment step, saidexpanded tubes being substantially hexagonal in cross-section andsubstantially all of the interstices between said tubes being occupiedby the expanded portions of the tubes.
 11. A method for making aglass-ceramic matrix comprising an assembly of integrally fused tubesforming a series of smooth, longitudinal parallel passagewaystherethrough, wherein the walls defining said passageways haveessentially zero porosity and an average coefficient of lineal thermalexpansion of about -12 to +12 X 10 7/*C., over the range 0*-300*C.,which comprises
 12. A method for making a glass-ceramic matrixcomprising an assembly of integrally fused tubes forming a series ofsmooth, longitudinal parallel passageways therethrough, wherein thewalls defining said passageways have essentially zero porosity and anaverage coefficient of lineal thermal expansion of about -12 to +12 X 107/*C., over the range 0*-300*C., which comprises
 13. A method for makinga glass-ceramic matrix comprising an assembly of integrally fused tubesforming a series of smooth, longitudinal parallel passagewaystherethrough, wherein the walls defining said passageways haveessentially zero porosity and an average coefficient of lineal thermalexpansion of about -12 to +12 X 10 7/*C., over the range 0 -3000*C.,which comprises
 14. A method for making a regenerator comprising aglass-ceramic matrix comprising an assembly of integrally fused tubesforming a series of smooth, longitudinal parallel passagewaystherethrough, wherein the walls defining said passageways haveessentially zero porosity and an average coefficient of lineal thermalexpansion of about -12 to +12 X 10 7/*C over the range 0*-300*C, whichcomprises
 15. The method for making a regenerator as defined in claim 14including the step of opening the sealed ends of the tubes in saidassembly of fused tubes after said tubes have expanded and prior tocontinuing with the next heat treatment step.
 16. The process accordingto claim 14 wherein assembly of integrally fused tubes is partiallycrystallized to a low expansion in the heat treatment step before step(6) and then cooled and the sealed ends of the tubes opened, beforereheating and effecting the heating and final crystallization step (6)recited in claim
 14. 17. The process according to claim 14 wherein saidglass tubes have a maximum inner diameter of 0.1 inch, and a wallthickness of about 0.015 inch to about 0.001 inch.
 18. A method formaking a regenerator comprising a glass-ceramic matrix comprising anassembly of integrally fused tubes forming a series of smooth,longitudinal parallel passageways therethrough, wherein the wallsdefining said passageways have essentially zero porosity and an averagecoefficient of lineal thermal expansion of about -12 to +12 X 10 7/*C,over the range of 0*-300*C, which comprises
 19. A method for making aglass-ceramic matrix comprising an assembly of integrally fused tubesforming a series of smooth, longitudinal parallel passagewaystherethrough, wherein the walls defining said passageways haveessentially zero porosity and an average coefficient of lineal thermalexpansion of about -12 to +12 X 10 7/*C over the range of 0*-300*C,which comprises